Earlier wheat drilling puts particular pressure on pre-ems this autumn

Despite growing grassweed problems across the country, many growers are keen to minimise their wheat establishment risks by drilling earlier than advisable for the best cultural control, reveals the latest in a series of national studies. This will put particular pressure on pre-em herbicides, making the most robust and resilient programmes more essential than ever.

Conducted by Gowan Crop Protection this summer, with more than 260 growers up and down the UK managing a total of just under 90,000ha of cropping, the 2022 National Grassweed Management Study spans a broad range of enterprises, establishment regimes and weed management practices.

It shows black-grass, ryegrass, brome and wild oat infestations continue to be widespread, with three quarters or more of growers having at least some problem with each, and more growers reporting an increase than a decrease in problems in each case (Figure 1).

“Interestingly, the proportion seeing increasing black-grass problems is lower than it was in a similarly comprehensive national survey conducted by Bayer in 2016,” points out study co-ordinator, Hank

King (pictured) of Gowan. “This clearly suggests the integrated approaches growers have been taking to deal with black-grass in recent years are having the desired e ect. “Unfortunately, the same cannot be said for bromes, ryegrass and wild oats, though. In all three cases, the proportion of growers seeing increasing problems with these weeds over the past four seasons is going up and the proportion reporting decreases going down. The situation is particularly worrying with ryegrass and wild oats.

“Equally concerning is the fact that problems with mixed grassweeds rather than just single species are reported by half of growers; especially so since control measures that work well with one species may not be the most appropriate for others.”

The 2022 study shows black-grass remaining the most signi cant grassweed issue for most growers, with nearly a quarter reporting problems across half or more of their winter cereals area and over a half across more than 10%. Wild oats are the second most problematic grassweed, with bromes and ryegrass somewhat less signi cant in their scale.

Black-grass with wild oats, and black-grass with bromes are the most widely encountered grassweed combinations, with wild oats proving a challenge in combination with other species for more than 50% of growers.

“Black-grass continues to be much more problematic in the south and east of the country than in the west and north,” Mr King notes. “If anything, though, the weed now appears to be more of an issue in the southern counties than in the historically worst-a ected eastern regions. And it remains most concerning under reduced tillage regimes.

“As well as in reduced tillage systems, bromes are especially problematic in both the southern and northern counties. While there are clear hotspots elsewhere, ryegrass problems are most widespread in the south and among those with shallow min till regimes. Wild oat problems, however, are more evenly distributed across the country and, like the other grassweeds, noticeably less under plough-based winter cereal establishment regimes.

“Herbicide resistant black-grass is continuing to cause issues for most growers, reveals the study, with over half reporting serious or very serious problems from resistance,” he adds. “Almost a quarter of growers are seeing similarly concerning resistance problems in ryegrass, with 16% nding issues that may be resistancerelated in bromes.” Grassweed Management Study

King (pictured) of Gowan. the integrated approaches growers have been taking to deal with black-grass in recent years are having the desired e ect.

“Unfortunately, the same

Figure 1: Changes in main grassweed problems

Percentage of growers seeing Increase No change Decrease

Black-grass 43% 35% 22%

Bromes 41% 45% 14%

Ryegrass

Wild oats 32%

26% 55%

48% 13%

24%

Cultural control

Of the 12 main cultural grassweed control techniques, the study reveals growers are currently employing an average of 9.7 in their management – an encouraging increase on the average of 6.3 of the same techniques identi ed in the 2016 survey.

The ve most widely used cultural grassweed controls – each employed by 85% or more of growers – continue to be spring cropping, stale seedbeds, delayed autumn drilling, rotational ploughing and increased seed rates. In all cases these are being more widely used than four years ago and are scored relatively highly for their e ectiveness by growers.

“With grassweed problems continuing to increase, it is worrying to see relatively large numbers of growers planning to drill their wheat earlier than advisable this season,” Mr King observes.

“Heeding the best advice, many growers are still setting mid-October as their target start date for wheat drilling on high grassweed risk elds to give time to spray-o the largest ushes of weed growth ahead of sowing. However, 52% are now

Percentage of growers planning to drill before mid-October

High weed risk elds 52%

Medium weed risk elds 80%

Low weed risk elds 93%

National Grassweed Management Study 2022 – Gowan.

...from previous page looking to drill high risk elds and 80% medium-risk elds before this time – presumably to minimise their establishment risk from the weather (Figure 2).

“This puts even more pressure on pre-em herbicides, making correct choice and use more critical than ever; not least given the dependence of most chemistry on both weather and seedbed quality for its performance.”

Pre-em performance

Regardless of claimed e cacy, soil-acting herbicide activity fundamentally depends on the season – primarily the weather. If conditions are too dry there isn’t enough moisture for most of today’s chemistry to work. Equally, if they’re too wet the herbicidal layer in the soil on which their activity depends is disrupted.

Extensive Gowan trials, for instance, show ve typical pre-em programmes – including the newest chemistry – giving an average black-grass control of 60% across 12 sites over the past four seasons, and varying from 50% to 68% between seasons.

Encouragingly, the addition of liquid tri-allate (Avadex Factor) to these programmes boosted average control to 74% while halving the season-to-season variation (Figure 3).

“Working as vapour in the air spaces within the soil rather than in the moisture ensures Avadex maintains as much e ectiveness as possible in drier seedbeds,” explains Mr King. “Its very low water solubility also means excessive rainfall has far less e ect on it than other chemistry.

“Added to this, tri-allate acts on multiple enzyme systems within the young plant to inhibit the synthesis of long chain fatty acids – including waxes. This means that weed seedlings not killed directly by the herbicide tend to emerge with substantially less leaf wax to interfere with the uptake of other chemistry.

“Growers and agronomists have long appreciated the extra black-grass, brome and ryegrass control value Avadex gives their pre-em programmes,” he concludes. “And it’s interesting to see this being maintained with the newest chemistry on the market.

“The season-proo ng Avadex Factor so clearly provides to pre-em programmes will be particularly valuable for those drilling wheat earlier than advisable this autumn.

“It will be most important under the reduced tillage regimes our study shows invariably have the greatest challenges from grassweeds. Also, where mixed grassweed populations, in general, and wild oat infestations, in particular, are problematic; not least because employing it in the autumn pre-em spray can frequently eliminate the need for subsequent wild oat spraying in the spring.” FG

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| @CHAPAgriTech Figure 3: Black-grass control from pre-em programmes 2019–2022

Average annual black-grass control % 90 85 80 75 70 65 60 55 50 45 Average 60% Range 50–68%

Base pre-em Average 74% Range 69–78%

Pre-em + Avadex Factor

Side-by-side comparisons of ve pre-em programmes with and without Avadex Factor at 12 sites over four years (Gowan).

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On-farm trials

Encouraging leap forward in black-grass control

The battle against black-grass could well be easier this autumn with a new grassweed herbicide now available from BASF.

Luximo is the brand name for cinmethylin – a completely new active with a new mode of action that has the potential to turn the tide for those battling with highly resistant strains of black-grass.

Having hosted trials at one of his client’s farms, independent agronomist, Richard Alcock, has seen Luximo perform across multiple seasons, on a population he knows well.

“We’ve put the trials in places where we know there will be a challenge,” he says. “It’s a good way of testing the product, and we’ve had some very good results.”

The trials have taken place at Nathan Hopkins’ farm in Yeovil in Somerset. It’s a business that’s grown rapidly since 2004, and now includes 1,200ha of arable land and 200ha of grassland. With four separate farms, soil types vary from Cotswold-type brash to very heavy clay.

“Nathan inherited a black-grass problem, when he took on some new business units,” explains Mr Alcock. “With quite a sizeable enterprise, spread across about seven miles, for economic and logistical reasons, we tend to block crop.”

The rotation on those blocks incorporates spring crops – either beans or barley – as well as winter oilseed rape and winter wheat.

“Machinery can easily spread weed seed around the four farms, so we have to be as clean as possible. As we can never eliminate the risk, we have to manage populations too. We also don’t want the problem building,” he says.

“We try to maximise late drilling. Where there is black-grass, the target drilling date for winter wheat is 25th October. Last year, we went at the beginning of the month because the forecast suggested that the weather was going to break and it would be unlikely that we’d get back onto the elds. As a result, the stale seedbeds didn’t work as well as we’d have liked, and we’ve more black-grass in some crops. In previous years, we’ve made the target drilling window and bene ted from lower seed return and lower black-grass populations.”

While delayed drilling is undoubtedly high on the list, for Mr Alcock it’s been changing the rotation that has had the biggest impact.

“We’ve dramatically reduced the second wheat area as it is a potential hotspot for increasing the black-grass problem. It’s not nearly as competitive as some of the hybrid barley that we grow and doesn’t have the same capacity for out-of-crop control.

“We’ve also increased seed rates, and where we used traditional vigorous non-inversion tillage going 5–6in deep, we’re now managing the seedbank in the top few inches of soil with minimum tillage.

“We encourage germination over the autumn and winter and spray o seedlings to reduce the weed burden. Those shallow cultivations are enough to create a seedbed in which we can direct drill with either the Horsch Serto Drill or a Sumo DTS Drill.

“We’ve been using this approach for so long that any seed down at depth will no longer be viable. Consequently, we’re now discussing rotational ploughing.”

The nal piece of the jigsaw, according to Mr Alcock, is the herbicide programme. With RRR resistant black-grass, in recent years that’s been Crystal or Liberator + d , followed by Avadex. Going forward, the programme will contain Luximo.

“Having seen Luximo in trials for three years now, I’ve con dence in the product and want it to play a central role in the pre-emergence stacks we apply.

“It’s proven to be a substantial step up for black-grass control, and I’ve already pre-ordered Luximo for the whole wheat acreage here.

“With resistant black-grass, the di erent mode of action is critical, but that is also something we need to protect by retaining the cultural controls and maximising its performance in any way that we can. The trials work at Mr Hopkins’ farm has contributed to the development of BASF’s o ering. According to BASF According to BASF agronomy manager, agronomy manager, Richard Guest (pictured), the replicated trials showed the value of pendimethalin as a partner to Luximo. This will be supplied in the pack as Stomp Aqua.

“We’ve had three years of trials here in various di erent elds,” he explains. “The sites had the perfect soil for black-grass with a high clay fraction that lies wet over the winter. The black-grass itself is as challenging as you’ll nd anywhere in the country – it’s RRR resistant.”

The team tested Luximo with a variety of partner products, comparing their performance against various standards such as Crystal + d and Liberator ( ufenacet and di ufenican) + aclonifen.

“Luximo’s performance here mirrored that of other trials; it was always incredibly high, consistently o ering more than 20 percentage points additional control.

“Extensive Luximo testing has found no direct cross resistance to any existing chemistry. These trials demonstrate how valuable that is in the eld.

“The trials also helped con rm Luximo’s place in the herbicide programme – pre-emergence has always been the best technical t. They also showed that partnering Luximo with pendimethalin is how to get the most control.”

“While Luximo o ers great improvements in herbicide control, the use of cultural controls such as spring cropping, delayed drilling, higher seeding rates, must come rst.” FG